1. Technical Field
The technical field relates to a light emitting diode (LED) and a fabricating method thereof, and particularly to an LED and a fabricating method thereof capable of enhancing a light extraction efficiency.
2. Description of Related Art
A light emitting diode (LED) is a semiconductor device constituted mainly by, for example, group III-V compound semiconductor materials. Since such semiconductor materials have a characteristic of converting electricity into light, when a current is applied to the semiconductor materials, electrons therein are combined with holes and excessive energy are released in form of light, thereby achieving an effect of luminosity.
Sapphire is often used as an epitaxy substrate in an LED, generally speaking. Since sapphire is a transparent material, an LED fabricated by using sapphire would scatter light to all directions without focusing the light and resulting in waste. Meanwhile, the scattered light is absorbed by each semiconductor layer inside the LED and heat is accumulated. Therefore, the emitting luminosity and efficiency of the gallium nitride (GaN) LEDs are lowered.
Additionally, since the GaN serving as the material for the epitaxial layer in the LED and sapphire substrates have mismatching lattice constants of around 16%, a large quantity of defects occurs at lattice growth junction, thus drastically weakening the luminous intensity. Moreover, the sapphire substrates adopted in conventional LEDs have lower heat dissipation coefficients than the GaN substrates, therefore due to the heat buildup, the luminous intensity is easily reduced.
Moreover, because of the difference between the indices of refraction of GaN and air, merely 4.54% of light generated in the LED can be successfully emitted from the GaN surface to the air. Therefore, the low light extraction efficiency causes drastic reduction in the external quantum efficiency of the LED, and accordingly the industry is earnestly pursuing an LED with high light extraction efficiency.